The purpose of the proposed experiments is to investigate aspects of secretion, transport, uptake and metabolism of lipoproteins in avian species. The triglyceride rich lipoprotein secreted into the venous drainage of the small intestine during infusion of labeled micellar solution will be isolated from the peripheral blood of conscious functionally hepatectomized birds. The hydrolytic activity of lipoprotein lipase will be controlled in some experiments by the injection prior to infusion of inhibitors. The primary particles secreted will be evaluated in terms of their particle size, chemical composition, electrophoretic mobility and immunological similarites with other plasma lipoproteins. In the absence of inhibitors of lipoprotein lipase, the previous experimental preparation will allow the isolation in relatively large quantities of partially degraded secondary particles for analyses and metabolic studies. Biologically labeled lipoprotein of defined particle sizes, prepared from the previously described preparation, will be employed to test the following hypotheses: 1) In the course of hydrolysis of the primary particle triglyceride in adipose tissue capillaries a gradual hydrolysis occurs resulting in a spectrum of smaller particles. This hypothesis is contrasted to the following alternative mechanism: The portomicrons are absorbed in the adipose tissue capillary bed and released after a finite hydrolysis of the particle triglyceride has occurred. 2) The primary particle triglyceride can be metabolized directly by the ovarian follicle rather than being first modified by the liver. In the process of uptake of either VLDL or primary particle triglyceride by oravian follicles, hydrolysis or partial hydrolysis of the molecule occurs. 3) Gonadotrophin hormones regulate the activity of follicular lipase involved in the hydrolysis of VLDL and primary particle triglyceride.